The invention concerns a screwed connection comprised of a threaded bolt, a nut, and a washer positioned between the nut and a surface of a component to be clamped.
Such screwed connections wherein the washer is engaged by a holding tool and the nut by a tightening tool are disclosed in EP 0 988 935 A2, EP 1 080 847 A2, and EP 1 435 279 A1.
According to EP 0 988 935 A2 a positive locking connection between the threaded bolt and the washer exists while according to EP 1 435 279 A1 a friction connection between the threaded bolt and the washer is provided. Additionally, according to EP 0 988 935 A2 a further holding element connected to the first holding element can positively engage the threaded bolt. In contrast to this, in the screwed connection according to EP 1 080 847 A2 there is no connection between the threaded bolt and the washer but holding tools that are connected to one another engage the washer as well as the threaded bolt in a positive locking way.
These prior art solutions have in common that the holding tool is supported on the washer as well as directly and/or indirectly on the threaded bolt to be tightened that therefore absorbs when tightening the nut the reaction forces of the screwing tool which forces are directed in a direction opposite to the tightening torque.
The frictional anti-rotation action of the washer relative to the threaded bolt according to EP 1 435 279 A1 can cause damage on the thread of the threaded bolt and thus lead to fatigue occurring too early. Moreover, the washer is designed in a special way so that its manufacture is complex.
The positive connection between the threaded bolt and the washer according to EP 0 988 935 A2 requires a matching configuration of the threaded bolt and, below the threaded part, it must be provided with one or several longitudinal grooves that are engaged by matching elements of the washer. In this way, the manufacture of the threaded bolt and of the washer is more complex and the fatigue strength of the threaded bolt may be impaired.
When in accordance with EP 0 988 935 A2 and EP 1 080 847 A2 a positive-locking engagement on the threaded bolt by means of a holding tool that, in turn, engages a holding tool engaging the washer is provided additionally, the arrangement is made more complicated and more complex.
The screw clamping force is determined in these known screwed connections by measuring the torque applied to the nut but this measurement is extremely imprecise because the frictional conditions in the screwed connection can fluctuate within a wide range as is well known in the art.